SVG path analysis in R

library(rgl)
knitr::knit_hooks$set(webgl = hook_webgl)

Scalable Vector Graphics, abbreviated: SVG, is an XML-based file format for static and dynamic vector graphics. It is an open standard of the W3C. Inkscape is an open source vector illustration program that uses the SVG format to store vector graphics. We start our analyses from checking Inkscape installation

This is the Scalable Vector Graphic we want to analyze:

url <- 'https://upload.wikimedia.org/wikipedia/commons/1/1b/Red_Bird.svg'
knitr::include_graphics(url)

As far there is no easy way to import SVG file, convert it into Simple Features and analyze using R. That’s why we gonna use an external powerful and beautiful tool which is Inkscape.

system('inkscape --version', intern = TRUE)

## [1] "Inkscape 1.2.1 (9c6d41e410, 2022-07-14)"

Simple Features from SVG

We can use dedicated R package https://github.com/JacekPardyak/inkscaper.

devtools::install_github("JacekPardyak/inkscaper")

## Skipping install of 'inkscaper' from a github remote, the SHA1 (7714a2a4) has not changed since last install.
##   Use `force = TRUE` to force installation

library(inkscaper)

Function to convert SVG into SF

logo <- url %>% 
  inx_svg2sf() %>%
  select(geometry) %>%
  st_union() %>%
  st_polygonize() %>% 
  first()

## Reading layer `entities' from data source 
##   `C:\Users\Jacek Pardyak\AppData\Local\Temp\RtmpKE1p46\inx_43c467547628.dxf' 
##   using driver `DXF'
## Simple feature collection with 2797 features and 6 fields
## Geometry type: LINESTRING
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA

logo %>% ggplot() +
  geom_sf()

result <- st_sfc() %>% st_sf(geometry = .)

for(i in c(1: length(logo))) {
  tmp <- logo %>% 
  nth(i) %>%
  st_sfc()  %>% st_sf(geometry = .) %>% mutate(facet = i)
  result <- tmp %>% bind_rows(result) 
}

result %>% ggplot() +
  geom_sf() +
  geom_sf_label(aes(label = facet)) +
  theme_void()

result %>% plot_ly(split = ~facet)

## No trace type specified:
##   Based on info supplied, a 'scatter' trace seems appropriate.
##   Read more about this trace type -> https://plotly.com/r/reference/#scatter

result %>% st_write("Red_Bird.shp", append=FALSE)

## Deleting layer `Red_Bird' using driver `ESRI Shapefile'
## Writing layer `Red_Bird' to data source `Red_Bird.shp' using driver `ESRI Shapefile'
## Writing 92 features with 1 fields and geometry type Polygon.

logo <- st_read("./Red_Bird.shp") %>% filter(!facet %in% 
                    c(3:55, 56:60, 81)) %>% st_union()

## Reading layer `Red_Bird' from data source 
##   `C:\Users\Jacek Pardyak\Documents\JacekPardyak.github.io\inkscaper\Red_Bird.shp' 
##   using driver `ESRI Shapefile'
## Simple feature collection with 92 features and 1 field
## Geometry type: POLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA

logo %>% ggplot() +
  geom_sf() +
  theme_void()

Surface from SVG

result <- st_read("./Red_Bird.shp") %>% filter(!facet %in% 
                    c(3:55, 56:60, 81)) %>% st_union() %>% st_sfc() %>% st_sf()

## Reading layer `Red_Bird' from data source 
##   `C:\Users\Jacek Pardyak\Documents\JacekPardyak.github.io\inkscaper\Red_Bird.shp' 
##   using driver `ESRI Shapefile'
## Simple feature collection with 92 features and 1 field
## Geometry type: POLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA

result

## Simple feature collection with 1 feature and 0 fields
## Geometry type: MULTIPOLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA
##                         geometry
## 1 MULTIPOLYGON (((55.96632 7....

result %>% ggplot() +
  geom_sf()

result

## Simple feature collection with 1 feature and 0 fields
## Geometry type: MULTIPOLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA
##                         geometry
## 1 MULTIPOLYGON (((55.96632 7....

grid_spacing = 1
grid <- result %>% st_make_grid(what = "centers", cellsize = c(grid_spacing, grid_spacing)) %>%
  st_sf() 

heights <- st_join(grid, (result %>% select(geometry) %>% mutate(Z = 1))) %>% replace(is.na(.), 0) 
z <- heights %>% st_coordinates() %>% as_tibble() %>% 
  bind_cols(heights %>% st_drop_geometry()) %>%
  mutate(X = round(X,1)) %>%
  mutate(Y = round(Y,1)) %>% pivot_wider(names_from = Y, values_from = Z) %>%
  column_to_rownames("X") %>% as.matrix()

x <- 1:nrow(z)  
y <- 1:ncol(z)  

colorlut <- c("#F2F2F2",  "#E34234") #"#ECB176",
col <- colorlut[ z - min(z) + 1 ] # assign colors to heights for each point

#open3d()
surface3d(x, y, z, color = col, back = "lines")

#e34234
#close3d()

Animation from SVG

library(gganimate)

result_1 <- st_read("./Red_Bird.shp") %>% filter(!facet %in% 
                    c(3:55, 56:60, 81)) %>% st_union() %>% st_sfc() %>% st_sf() %>% 
  mutate(facet = 1)

## Reading layer `Red_Bird' from data source 
##   `C:\Users\Jacek Pardyak\Documents\JacekPardyak.github.io\inkscaper\Red_Bird.shp' 
##   using driver `ESRI Shapefile'
## Simple feature collection with 92 features and 1 field
## Geometry type: POLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA

result_2 <- st_read("./Red_Bird.shp") %>% filter(facet %in% 
                    c(3:55, 56:60, 81)) %>% st_union() %>% st_sfc() %>% st_sf() %>% 
  mutate(facet = 2)

## Reading layer `Red_Bird' from data source 
##   `C:\Users\Jacek Pardyak\Documents\JacekPardyak.github.io\inkscaper\Red_Bird.shp' 
##   using driver `ESRI Shapefile'
## Simple feature collection with 92 features and 1 field
## Geometry type: POLYGON
## Dimension:     XY
## Bounding box:  xmin: 22.41016 ymin: 5.324796 xmax: 103.6297 ymax: 87.57702
## CRS:           NA

result <- result_1 %>% bind_rows(result_2)
result %>% ggplot() +
  geom_sf()  + 
  transition_states(
    facet,
    transition_length = 2,
    state_length = 1
  ) +
  enter_fade() + 
  exit_shrink() +
  ease_aes('sine-in-out')

Appendix A - Inkscape Actions

While obviously Inkscape is primarily intended as a GUI application, it can be used for doing SVG processing on the command line as well. Inkscape Actions available in versions Inkscape 1.2.1 (9c6d41e410, 2022-07-14) are listed below.

Appendix B - Inkscape Extensions

Inkscape Extensions are small programs that extend Inkscape’s functionality. They can provide features for specific tasks, experimentation, or art styles. They can also add support for special hardware or different export formats. While many extensions are included with Inkscape, you can also install extensions written by third parties or write your own. The table below shows the list of extensions available in Inkscape of version Inkscape 1.2.1 (9c6d41e410, 2022-07-14) with descriptions.

Appendix C - Inkscape Help

Result of the call system('inkscape --help', intern = TRUE)

## [1] "Usage:"
## [1] "  org.inkscape.Inkscape [OPTION…] file1 [file2 [fileN]]"
## [1] ""
## [1] "Process (or open) one or more files."
## [1] ""
## [1] "Help Options:"
## [1] "  -?, --help                                 Show help options"
## [1] "  --help-all                                 Show all help options"
## [1] "  --help-gapplication                        Show GApplication options"
## [1] "  --help-gtk                                 Show GTK+ Options"
## [1] ""
## [1] "Application Options:"
## [1] "  -V, --version                              Print Inkscape version"
## [1] "  --debug-info                               Print debugging information"
## [1] "  --system-data-directory                    Print system data directory"
## [1] "  --user-data-directory                      Print user data directory"
## [1] "  --app-id-tag                               Create a unique instance of Inkscape with the application ID 'org.inkscape.Inkscape.TAG'"
## [1] "  --\b\b  "
## [1] "File import:                        "
## [1] "  -p, --pipe                                 Read input file from standard input (stdin)"
## [1] "  --pdf-page=PAGE                            PDF page number to import"
## [1] "  --pdf-poppler                              Use poppler when importing via commandline"
## [1] "  --convert-dpi-method=METHOD                Method used to convert pre-0.92 document dpi, if needed: [none|scale-viewbox|scale-document]"
## [1] "  --no-convert-text-baseline-spacing         Do not fix pre-0.92 document's text baseline spacing on opening"
## [1] "  --\b\b  "
## [1] "File export:                        "
## [1] "  -o, --export-filename=FILENAME             Output file name (defaults to input filename; file type is guessed from extension if present; use '-' to write to stdout)"
## [1] "  --export-overwrite                         Overwrite input file (otherwise add '_out' suffix if type doesn't change)"
## [1] "  --export-type=TYPE[,TYPE]*                 File type(s) to export: [svg,png,ps,eps,pdf,emf,wmf,xaml]"
## [1] "  --export-extension=EXTENSION-ID            Extension ID to use for exporting"
## [1] "  --\b\b  "
## [1] "Export geometry:                    "
## [1] "  -C, --export-area-page                     Area to export is page"
## [1] "  -D, --export-area-drawing                  Area to export is whole drawing (ignoring page size)"
## [1] "  -a, --export-area=x0:y0:x1:y1              Area to export in SVG user units"
## [1] "  --export-area-snap                         Snap the bitmap export area outwards to the nearest integer values"
## [1] "  -d, --export-dpi=DPI                       Resolution for bitmaps and rasterized filters; default is 96"
## [1] "  -w, --export-width=WIDTH                   Bitmap width in pixels (overrides --export-dpi)"
## [1] "  -h, --export-height=HEIGHT                 Bitmap height in pixels (overrides --export-dpi)"
## [1] "  --export-margin=MARGIN                     Margin around export area: units of page size for SVG, mm for PS/PDF"
## [1] "  --\b\b  "
## [1] "Export options:                     "
## [1] "  -i, --export-id=OBJECT-ID[;OBJECT-ID]*     ID(s) of object(s) to export"
## [1] "  -j, --export-id-only                       Hide all objects except object with ID selected by export-id"
## [1] "  -l, --export-plain-svg                     Remove Inkscape-specific SVG attributes/properties"
## [1] "  --export-ps-level=LEVEL                    Postscript level (2 or 3); default is 3"
## [1] "  --export-pdf-version=VERSION               PDF version (1.4 or 1.5); default is 1.5"
## [1] "  -T, --export-text-to-path                  Convert text to paths (PS/EPS/PDF/SVG)"
## [1] "  --export-latex                             Export text separately to LaTeX file (PS/EPS/PDF)"
## [1] "  --export-ignore-filters                    Render objects without filters instead of rasterizing (PS/EPS/PDF)"
## [1] "  -t, --export-use-hints                     Use stored filename and DPI hints when exporting object selected by --export-id"
## [1] "  -b, --export-background=COLOR              Background color for exported bitmaps (any SVG color string)"
## [1] "  -y, --export-background-opacity=VALUE      Background opacity for exported bitmaps (0.0 to 1.0, or 1 to 255)"
## [1] "  --export-png-color-mode=COLOR-MODE         Color mode (bit depth and color type) for exported bitmaps (Gray_1/Gray_2/Gray_4/Gray_8/Gray_16/RGB_8/RGB_16/GrayAlpha_8/GrayAlpha_16/RGBA_8/RGBA_16)"
## [1] "  --export-png-use-dithering=false|true      Force dithering or disables it"
## [1] "  --\b\b  "
## [1] "Query object/document geometry:     "
## [1] "  -I, --query-id=OBJECT-ID[,OBJECT-ID]*      ID(s) of object(s) to be queried"
## [1] "  -S, --query-all                            Print bounding boxes of all objects"
## [1] "  -X, --query-x                              X coordinate of drawing or object (if specified by --query-id)"
## [1] "  -Y, --query-y                              Y coordinate of drawing or object (if specified by --query-id)"
## [1] "  -W, --query-width                          Width of drawing or object (if specified by --query-id)"
## [1] "  -H, --query-height                         Height of drawing or object (if specified by --query-id)"
## [1] "  --\b\b  "
## [1] "Advanced file processing:           "
## [1] "  --vacuum-defs                              Remove unused definitions from the <defs> section(s) of document"
## [1] "  --select=OBJECT-ID[,OBJECT-ID]*            Select objects: comma-separated list of IDs"
## [1] "  --\b\b                                       "
## [1] "  --actions=ACTION(:ARG)[;ACTION(:ARG)]*     List of actions (with optional arguments) to execute"
## [1] "  --action-list                              List all available actions"
## [1] "  --\b\b  "
## [1] "Interface:                          "
## [1] "  -g, --with-gui                             With graphical user interface (required by some actions)"
## [1] "  --batch-process                            Close GUI after executing all actions"
## [1] "  --\b\b                                       "
## [1] "  --shell                                    Start Inkscape in interactive shell mode"
## [1] ""
## [1] ""
## [1] "Examples:"
## [1] "  Export input SVG (in.svg) to PDF (out.pdf) format:"
## [1] "\tinkscape --export-filename=out.pdf in.svg"
## [1] "  Export input files (in1.svg, in2.svg) to PNG format keeping original name (in1.png, in2.png):"
## [1] "\tinkscape --export-type=png in1.svg in2.svg"
## [1] "  See 'man inkscape' and http://wiki.inkscape.org/wiki/index.php/Using_the_Command_Line for more details."